The reasons for investigating, exploring or inspecting the subsurface environment are almost endless in number. A borehole is an artificial excavation typically made to extract water, oil, gas and other materials from the earth. There of course is also the use of boreholes for exploration and inspection purposes. For example, boreholes are drilled in the earth to locate mineral or gas or oil deposits, to help locate the most accessible ground water reservoirs, geothermal supplies, and to check for subsurface integrity and stability for location of depositories for nuclear waste and other materials that require underground storage. Additionally, the demand for ground water resources has accelerated so rapidly in recent years that the demand is at a point where new sources of high quality water are increasingly difficult to find since so many of the most accessible reservoirs are already tapped and utilized. Thus utilization of a variety exploration techniques is essential in locating new aquifers of high quality water. Additionally, the measuring of fluid movement within the subsurface can be of great significance. Thus, the need to characterize subsurface conditions is of immense commercial and environmental importance.
It is of course possible, in large diameter boreholes, to physically lower a trained geologist into the hole with a light source to visually examine the stratification, fracturing and layering of various geological formations to the depth that the borehole penetrates. However, such a technique has severe limitations from both a practical and safety standpoint. A significant advance has been made by virtue of closed circuit television camera systems for visually examining the walls of a given borehole. Television cameras measuring as small as 1 1/2 inches in diameter are capable of surveying deep into holes to provide sharp images of actual subsurface conditions. Such cameras are designed to meet the inspection needs of the ground water industry; gas, oil and mining industries; public works officials; environmentalists and others in pinpointing problems. Such cameras can assist in analyzing geologic strata in ground formations, study variations in soil coloration to ascertain chemical and mineral content, detect damage in underground petroleum storage tanks and piping, as well as to help provide visual proof of compliance with various governmental inspection requirements.
Although such television inspection systems are frequently used in boreholes to analyze and inspect geologic strata, ground formations and the like, soil conditions or borehole collapse because of cave-ins, either prevents use of such equipment entirely, or in some cases results in the equipment being trapped in a borehole with possible loss or damage to the equipment, or at the very least the expenditure of considerable effort in recovery.
Such photographic equipment has, of course, also been used to inspect the interior of well casings to locate corrosion, obstructions, incrustations and generally to determine the condition of such casings; also to verify the success of cleaning and repair procedures. However, because of the opaque nature of casing materials, it is not possible for such inspection systems to inspect any area other than the interior of the casing.
Accordingly it is a principal object of this invention to provide a method for inspecting subsurface environments through the use of a borehole or other artificial excavation whereby integrity of the borehole is maintained and photographic equipment or other inspection means can be employed to inspect such environments without danger of loss or damage.
It is a further object of this invention to provide a method for allowing for visual inspection of the exterior of previously emplaced casings, either on a temporary or permanent basis.
It is a still further object of this invention to provide a casing which allows for visual inspection of not only the interior of the casing but the environment surrounding the casing as well.
These and other objects and advantages of this invention will become more apparent in the following description and appended claims.